Acousto-electric signal translation system

ABSTRACT

A body of piezoelectric material propagates acoustic surface waves. For launching or absorbing those waves, an electrode array is coupled to a surface portion of the body. The array includes a bifilar coil comprising a pair of windings coiled over the surface. A source or load is coupled between one end of one winding and the remote end of the other winding, with the remaining ends of both windings coupled together. The spacing between adjacent turns of the windings is effectively one-half the wavelength of the acoustic waves at the operating frequency. The bifilar winding is shown either in a form where it is coiled around a cylinder or where it is nested concentrically on a surface. In one species, an input transducer launches waves in two directions around a cylinder, and an output transducer absorbs waves coming from both of the two directions. The bifilar coil contributes an inductive reactance to compensate the clamped capacitance of the transducer.

United States Patent [72] Inventors Adrian J. De Vries Elmhurst;

Fleming Dias, Chicago, both of III. [21] Appl. No. 710,118 [22] FiledMar. 4, 1968 [45] Patented Sept. 28, 1971 [73] Assignee Zenith RadioCorporation Chicago, Ill.

[54] ACOUSTO-ELECTRIC SIGNAL TRANSLATION SYSTEM 7 Claims, 3 DrawingFigs.

[52] [1.8. CI 333/72, 33 3/30 [51] Int. Cl 03h 9/00 [50] Field ofSearch333/30, 72; 3 30/4.9

[56] References Cited UNITED STATES PATENTS 3,187,192 6/1965 Nalos330/4.9 3,300,739 l/1967 Mortley. 333/72 3,401,360 9/1968 Du Bois.333/30 3,360,749 12/l967 Sittig 333/30 3,369,199 2/1968 Sittig 333/30Primary ExaminerHerman Karl Saalbach Assistant ExaminerC. BaraffAttorneys-Francis W. Crotty and Hugh H. Drake ABSTRACT: A body ofpiezoelectric material propagates acoustic surface waves. For launchingor absorbing those waves, an electrode array is coupled to a surfaceportion of the body. The array includes a bifilar coil comprising a pairof windings coiled over the surface. A source or load is coupled betweenone end of one winding and the remote end of the other winding, with theremaining ends of both windings coupled together. The spacing betweenadjacent turns of the windings is effectively one-half the wavelength ofthe acoustic waves at the operating frequency. The bifilar winding isshown either in a form where it is coiled around a cylinder or where itis nested concentrically on a surface. In one species, an inputtransducer launches waves in two directions around a cylinder, and anoutput transducer absorbs waves coming from both of the two directions.The bifilar coil contributes an inductive reactance to compensate theclamped capacitance of the transducer.

PATENIEUSEP28I9H 3.609.602

Inventors Adrian J. De Vries Fleming Dias ACOUSTO-ELECTRIC SIGNALTRANSLATION SYSTEM This invention pertains to signal translationsystems. More particularly, it relates to solid-state circuitryincluding an acoustoelectric transducing arrangement which involvesinteraction between transducer elements coupled to a piezoelectricmaterial and acoustic waves propagated in that material.

In copending application Ser. No. 582,387, filedSept. 27, 1966 nowabandoned, there are disclosed and claimed a number of differentembodiments of acoustoelectric devices in which acoustic surface wavespropagating in a piezoelectric material interact with transducerscoupled to the surface waves. In each of the embodiments particularlydisclosed in that application, surface waves launched in the body ofpiezoelectric material are caused, in one manner or another, to interactwith a second transducer spaced along the surface from the first. In thesimplest case, the firsttransducer is coupled to a source of signalswhile the second transducer is coupled to a load, the signal energybeing translated by the acoustic waves between the two transducers.

In operation, the transducers exhibit a clamped capacitance which may bedeterminative of the magnitude of impedance the transducers are capableof presenting to the associated circuitry. The clamped capacitance maybe defined as that capacitance exhibited when all mechanical motion isinhibited. When utilizing these devices, that clamped capacitanceheretofore has been tuned out or compensated by the use of externalinductors.

It is the general object of the present invention to provide a new andimproved signal translation system of the aforesaid acoustoelectricvariety and in which the clamped capacitance is compensated without theneed for external elements.

It is another object of the present invention to provide a new andimproved acoustoelectric signal translation system of the foregoingcharacter which is capable of being fabricated with either a curved or aplanar surface over which the waves are translated.

A further object of the present invention is to provide a new improvedsignal translation system in which acoustic waves launched in twodifferent directions by an input transducer are effectively absorbed andutilized by an output transducer.

A related object of the present invention is to provide such a device inwhich interference from acoustic waves launched in a second direction isavoided.

In accordance with one aspect of the present invention, anacoustoelectric signal translation system includes a source of signalsat a predetermined frequency and a body of piezoelectric materialpropagative of acoustic surface waves along the body. The array includesa bifilar coil comprising first and second windings coiled over thesurface with the two windings interleaved. The signal source is coupledbetween one end of one of the windings and the remote end of the otherwinding while the remaining ends of both windings are coupled to oneanother. The center-to-center spacing of adjacent turns of the bifilarcoil is effectively one-half the wavelength of the acoustic waves at thedesired signal frequency. Finally, the system includes interaction meanscoupled to a second portion of the body spaced from the first andresponsive to the launched acoustic waves for utilizing the signalenergy translated thereby.

With regard to another aspect of the present invention the transducerdisposed on the first portion of the piezoelectric body responds toinput signals and launches acoustic waves respectively along each one ofa pair of paths individually extending in different directions from thetransducer. Interaction means, coupled to the second portion of the bodyand disposed in both of the aforesaid paths, responds simultaneously tothe acoustic waves launched in both paths to utilize the signal energytranslated by such waves.

The features of the present invention which are believed to be novel areset forth with particularity in the appended claims. The organizationand manner of operation of the invention, together with further objectsand advantages thereof, may best be understood by reference to thefollowing description taken in conjunction with the accompanyingdrawing, in the several figures of which like reference numeralsidentify like elements and in which:

FIG. 1 is a diagram of one embodiment of a signal translation systemembodying the invention;

FIG. 2 is a diagram of an alternative embodiment of such a system; and

FIG. 3 is a diagram of yet another alternative embodiment of such asignal translation system.

In FIG. 1, a signal source 10 is coupled between terminals 11 and 12 ofan input transducer 13. Transducer 13 is coupled to the major surface ofa piezoelectric body 14 in this case in the shape of an elongatedcylindrical rod. The transducer is constructed of a bifilar coilcomprising first and second windings l5 and 16 coiled over the surfaceof body 14 with their individual turns distributed thcrealong so as toconstitute an electrical array. By way of terminal 11 and 12, source 10is coupled between one end of winding 15 and the other or remote end ofwinding 16. The remaining end of winding 15 has a terminal 17, and theremaining end of winding 16 has a terminal 18, and terminals l7, 18 arecoupled together, in this case by both being connected to ground.Further, the centerto-center spacing of adjacent turns of the set ofwindings 15 and 16, that is to say the center-to-center spacing ofadjacent turns of the bifilar coil, is one-half of the designed acousticwavelength, in the material of body 14, of the signal wave for which itis desired to achieve maximum response. windings 15 and 16 are formed ofa material such as gold which may be vacuum deposited, or plated andthen etched, upon the exterior surface of a polished piezoelectric bodyof a a material such as PZT (lead zirconate titanate) or otherpiezoelectric material having similar properties.

When PTZ is used as the piezoelectric material, it preferably ispolarized so that the cylindrical axis of body 14 is the axis ofelectrical symmetry. This may be accomplished by polarizing the materialeither radially or in the direction of the cylindrical axis. For radialpolarization, a rod-type electrode is embedded in the rod with its axiscoinciding with the cylindrical axis of body 14, and the otherpolarizing electrode is formed by depositing a conductive layer on theexternal cylindrical surface of body 14; that layer is removed followingpolarization. Axial polarization may be achieved by affixing thepolarizing electrodes to opposing ends of body 14.

PTZ is particularly attractive as the material for body 14 because itshigh permittivity (about 1,000) permits the use of comparatively smallcoils in transducer 13 to achieve the results to be further described.Alternatively, zinc oxide may be used; its so-called c-axis is orientedto be parallel with the cylindrical axis of body 14.

With the described arrangement transducer 13 is composed of interleavedconductive stripes to which source 10 feeds alternating electricpotentials. It is known that a transducer of that general nature, whencoupled to a piezoelectric medium, produces acoustic surface waves onthe medium which, in the simplified isotropic case of a ceramic poledperpendicularly to the surface, travel at right angles to the stripes.Thus, in operation, direct piezoelectric surface wave transduction isaccomplished by the spatially periodic interdigital electrodes oftransducer 13 and specifically by the periodic electric fields createdbetween those electrode stripes in response to a signal from source 10of a frequency such that the wavelength of the acoustic wavescorresponds to the center-to-center spacing of two adjacent turnsbelonging to the same one of the interleaved windings 15,16. Thispiezoelectric coupling to the surface waves occurs when the straincomponents produced by the electrical fields in the piezoelectricmaterial are substantially matched to the strain components associatedwith the surface wave mode. Source 10, for example the front end of atelevision receiver, may produce a range of LP. signal frequencies forapplication to IF amplifier and video system 21. However, by reason ofthe selective nature of transducer 13, only a narrow range offrequencies corresponding to the desired IF bandwidth are converted tosurface wave energy. The result is that transducer 13 and piezoelectricbody 14 constitute a filter.

The kind of waves produced by transducer 13 generally may be describedas being in the known Rayleigh wave mode. However, waves so travelingover a curved surface are not pure Rayleigh waves but when the diameterof body 14 is large relative to the acoustic wavelength, the surface maybe considered to be essentially flat and the wave action approaches thatof the Rayleigh condition.

Because it is composed of spaced elements of conductive materialseparated by a dielectric, transducer 13 exhibits, as seen acrossterminals 11 and 12, that which has been described as the clampedcapacitance. By connecting the windings as described and illustrated,not only is the desired electric field created between adjacent turns soas to launch the surface waves, but the magnetic flux lines encircled bythe turns are in a direction to reenforce one another. Consequently, thebifilar winding arrangement also develops compensating inductance whichappears between terminals 1 1 and 12. More particularly, the clampedcapacitance of transducer 13 is distributed along the interleavedwindings. To achieve compensation of that 21. At The number of turns ofbifilar coil 13 and the pitch of the coil turns are selected tocontribute an amount of inductive reactance for compensation purposescompatible with the desired bandwidth of the transducer. In other words,this in practical structures is a matter of compromise although ideallythe input impedance, presented across terminals 11 and 12, is real atthe frequency of maximum response of the electroacoustic array.

The acoustic waves launched by transducer 13 may be absorbed andutilized directly and for that purpose FIG. 1 incorporates a secondtransducer structurally similar to transducer 13 and responsive to theacoustic waves. Thus, an output transducer 20 likewise is formed bycoiling a bifilar winding around the other end portion of thecylindrical rod 14 of piezoelectric material. A load 21 is coupledbetween one end 22 of one winding 25 of the output transducer coil. Theremaining end 27 of winding 23 is coupled to the remaining end 24 ofwinding 25 by virtue of their common connection to ground. AS before,the center-to-center spacing between adjacent turns of the bifilarwinding in output transducer 20 is one-half of the acoustic wavelenghthin the piezoelectric material of the signal wave for which maximumresponse is desired. In operation, transducer 20 absorbs energy from thesurface waves launched by transducer 13 and feeds it to load 21. At thesame time, the winding arrangement is such that it creates an inductivereactance which is employed to compensate fully or partially the clampedcapacitance of transducer 20. The winding turns in transducer 13 areparallel to those in transducer 20.

The FIG. 2 embodiment is similar in that it includes an input transducer30 which launches surface waves along a piezoelectric substrate 31 to anoutput transducer 32. In this case, however, the wave propagatingsurface of substrate 31 is planar and transducers 30 and 32 are composedof bifilar coils comprising a pair of windings having a flat or pancakeeonfiguration with winding turns nested concentrically on the surface ofsubstrate 31. For convenience, the input signal source and the load havebeen omitted from FIG. 2 but, as in the case of FIG. 1, those devicesare coupled between one end of one winding and the remote end of theother winding while the remaining ends of both windings are coupledtogether. Thus, the input signal energy may be applied between theterminal 33 of one winding 34 and the remote terminal 35 of the otherwinding 36. The remaining two terminals 370 and 37b are then coupledtogether to complete the circuitry. Similarly, the signal energy derivedfrom transducer 32 is taken across a terminal 38 of one winding 39 ofthe bifilar coil and the remote terminal 40 of other winding 41 of thebifilar coil. As before, the remaining terminals 42a and 42b of winding39, 40 are coupled together. Transducers 30 and 32 may be formed byvacuum depositing or plating and, as is often done when printingcircuits, the terminals may be formed merely by depositing I or leavingan enlarged area integral with the strips and to which the connectionsare made.

In the case of either transducer 13 in FIG. 1 or transducer 30 in FIG.2, the potentials developed between adjacent turns of the windingsproduce a dominant pair of waves traveling longitudinally along thesurface of the piezoelectric material in opposing directionsperpendicular to the stripes for the illustrated isotropic case and aminor pair of waves traveling normally to the first. A fraction of thedominant waves pass through the output transducer. Accordingly, in thedevices of FIGS. 1 and 2 it may be desirable to include means forattenuating the nonutilized one of the dominant waves, or the wavepassed by the output transducer, and also the minor pair of waves inorder to prevent unwanted subsequent interaction with reflected waves.To this end, all peripheral portions of the piezoelectric material maybe formed to have an irregular contour, as indicated and as a result ofwhich the waves are scattered and consequently attenuated in a pluralityof noncoherent reflections.

In the embodiment of FIG. 2, each transducer 30, 32 may be thought of ashaving equal and separated left and right portions as viewed in thedrawing with the dividing line of such portions perpendicular to thepropagation direction. It is desirable that surface waves generated bythe left portion of the transducer be enhanced by surface wavesgenerated by the other or right portion of the same transducer. Thegeneral condition to be This loss is that turns belonging to the samewinding, for instance winding 34 of transducer 30, are positioned suchbifilar the center-to-center spacing of successive turns of that windingis a full wavelength of the acoustic wave. It may also be noted that,for increased selectivity, additional electrode turns may be added tothe bifilar transducer. Still additionally, in the arrangement of FIG. 2some energy is lost by reason of the generation of waves heretoforereferred to as the minor pair traveling in directions perpendicular to aline joining the input and output transducer. Thisloss may be reduced byforming the coils to have a large aspect ratio, that is, to form thebifilar coils to have a width, perpendicular to the direction of desiredwave travel, large compared to .the dimension in the direction of wavetravel.

Another approach with respect to the second of the two acoustic waveslaunched by an input transducer is that of FIG. 3 which actuallyutilizes both of the pair of dominant waves simultaneously. To this end,an input transducer 50 is disposed on the exterior cylindrical surfaceportion of a piezoelectric element 51 which is cylindrical in shape.Diametrically opposite input transducer 50 is an output transducer 52.Consequently, the dominant pair of acoustic surface waves developed bytransducer 50 in response to input signals are launched respectivelyalong each one of a pair of paths 53 and 54 which extend individually indifferent directions from transducer 50. Output transducer 52 isdisposed in both of paths 53 and 54 so as to respond simultaneously tothe acoustic waves traveling along both paths.

Transducers 50 and 52 may be placed upon either the interior or exteriorcurved surfaces of cylindrical element 51. The exterior curved surfaceis preferred because it is known that surface waves propagating overinterior curved surfaces suffer attenuation by virtue of conversion tobulk waves. In either case, the winding turns are nested concentricallyon the surface and the bifilar coil as a whole is given a slightcurvature so as to lie flat against the curved surface of thepiezoelectric element. Consequently, transducers 50 and 52 are ofessentially the same general configuration as in FIG. 2 with the windingturns nested concentrically upon a surface of element 51. The inputsignal source and the load, as well as the individual windingconnections to each of transducers 50 and 52, which have not been shown,are the same as described above with respect to FIG. 2.

As indicated in FIG. 3, a cylindrical metallic core 55 mayadvantageously be provided for piezoelectric element Sl. It may serve,for example, as one of the pair of electrodes required to polarizeelement 51. After the polarizing has been accomplished, the other oreexternal electrode (not shown) of the pair is removed and the inner one55 is retained to constitute an electrostatic shield between transducers50 and 52. It may also aid in physically supporting the acoustic systemin its operating relation to other devices. If desired, the surfaceportions of element which support transducers 50 and 52 may be flattenedto facilitate mounting the transducers.

The arrangements disclosed permit the formation of surface wavetransducers in a manner inherently creating an inductive reactanceuseful in compensating the clamped capacitance necessarily associatedwith the use of a plurality of spaced electrodes. The principle involvedis applicable to transducing arrangements of either a curved or agenerally fiat configuration, thus giving rise to a wide variety ofdifferent device configurations. Being entirely of a solid state nature,the arrangements discussed likewise lend themselves admirably tocomplete integration of circuitry and device. in addition the overallarrangement of FIG. 3 permits positive positive utilization of both thedominant waves necessarily developed by an acoustic wave transducer ofthe array type.

While particular embodiments of the present invention have i been shownand described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from theinvention in its broader aspects. Accordingly, the aim in the appendedclaims is to cover all such changes and modifications as fall within thetrue spirit and scope of the invention.

We claim:

1. An acoustoelectric signal translation system comprising:

a source of signals of a predetermined frequency;

a body of piezoelectric material propagative of acoustic surface waves;

a first electrode array coupled to a first surface portion of said bodyand responsive to said signals for launching acoustic surface wavesalong said body, said array including a bifilar coil comprisinginterleaved first and second windings coiled over said surface with saidsource coupled between one end of one of said windings and the remoteend of the other of said windings, the remaining ends of said windingsbeing coupled to one another, and

I the spacing between adjacent turns of said bifilar coil beingeffectively one-half the wavelength of the acoustic waves at saidpredetermined frequency;

and interaction means coupled to a second portion of said body spacedfrom said first portion, responsive to said launched acoustic waves forderiving the signal energy translated thereby.

2. A system as defined in claim 1 in which said interaction meansincludes:

a second electrode array including another bifilar coil comprisinginterleaved third and fourth windings coiled over said surface with thespacing between adjacent turns of said other bifilar coil beingeffectively one-half the wavelength of the acoustic waves at saidpredetermined frequency;

a load coupled between one end of said third winding and the remote endof said fourth winding;

and means for connecting the remaining ends of said third and fourthwindings to the remaining ends of said first and second windings.

3. A system as defined in claim 1 in which said body is of elongatedcylindrical shape and said bifilar coil is coiled around the cylindricalsurface of said body.

4. A system as defined in claim 1 in which said body includes agenerally planar surface on which said transducer is disposed with saidbifilar coil of generally flat configuration and having the windingturns thereof nested concentrically on said surface.

5. A system as defined in claim 1 in which said body is of cylindricalshape and said bifilar winding has its turns nested concentrically on anouter peripheral surface of said body to launch said acoustic wavesalong a curved path over said surface.

6. A system as defined in claim 1 in which said bifilar coil contributesinductive reactance substantially compensatory of the clampedcapacitance created by said windings and said body.

7. An acoustoelectric signal translation system comprising:

a generally cylindrical body of piezoelectric material propagative ofacoustic waves;

a surface wave transducer disposed on a first peripheral portion of saidbody and responsive to input signals for launching acoustic surfacewaves respectively along each one of a pair of circumferential pathsindividually extending in opposite directions from said transducer;

and interaction means, comprising a second surface wave transducercoupled to a second peripheral portion of said body spaced from saidfirst peripheral portion and disposed in both of said paths, responsiveto said launched acoustic surface waves in both paths for utilizing thesignal energy translated thereby, in which said body is a hollowcylinder and in which a conductive metallic core extends axially throughsaid body to serve as a shield between said transducers.

2. A system as defined in claim 1 in which said interaction meansincludes: a second electrode array including another bifilar coilcomprising interleaved third and fourth windings coiled over saidsurface with the spacing between adjacent turns of said other bifilarcoil being effectively one-half the wavelength of the acoustic waves atsaid predetermined frequency; a load coupled between one end of saidthird winding and the remote end of said fourth winding; and means forconnecting the remaining ends of said third and fourth windings to theremaining ends of said first and second windings.
 3. A system as definedin claim 1 in which said body is of elongated cylindrical shape and saidbifilar coil is coiled around the cylindrical surface of said body.
 4. Asystem as defined in claim 1 in which said body includes a generallyplanar surface on which said transducer is disposed with said bifilarcoil of generally flat configuration and having the winding turnsthereof nested concentrically on said surface.
 5. A system as defined inclaim 1 in which said body is of cylindrical shape and said bifilarwinding has its turns nested concentrically on an outer peripheralsurface of said body to launch said acoustic waves along a curved pathover said surface.
 6. A system as defined in claim 1 in which saidbifilar coil contributes inductive reactance substantially compensatoryof the clamped capacitance created by said windings and said body.
 7. Anacoustoelectric signal translation system comprising: a generallycylindrical body of piezoelectric material propagative of acousticwaves; a surface wave transducer disposed on a first peripheral portionof said body and responsive to input signals for launching acousticsurface waves respectively along each one of a pair of circumferentialpaths individually extending in opposite directions from saidtransducer; and interaction means, comprising a second surface wavetransducer coupled to a second peripheral portion of said body spacedfrom said first peripheral portion and disposed in both of said paths,responsive to said launched acoustic surface waves in both paths forutilizing the signal energy translated thereby, in which said body is ahollow cylinder and in which a conductive metallic core extends axiallythrough said Body to serve as a shield between said transducers.